A known electrophotographic image forming apparatus is arranged such that the surface of a photoreceptor is uniformly charged by means of a front charger while the photoreceptor being rotated; light such as laser beams is projected onto the surface of the photoreceptor from an optical system to form an electrostatic latent image; toner is adhered to the electrostatic latent image in a developing section to form a toner image on the surface of the photoreceptor; the toner image is transferred onto a paper sheet in a transferring section; and the toner image thus transferred is then fixed to the paper sheet in a fixing section.
Most of recent developing units for use with an electrophotographic image forming apparatus having the above-described arrangement are provided with a plurality of stirring paddles and magnet rollers in the main body thereof. In such a developing unit, developer consisting of a mixture of toner and carrier is stored in the main body of the developing unit. The developer is stirred with the stirring paddles so as to be charged by friction and adhered onto the surface of a magnet roller in the form of a magnetic brush, whereby the developer is transferred to the side of the photoreceptor. In this stage, toner is supplemented from a toner hopper to the main body of the developing unit in accordance with the consumption of toner. Although carrier is repeatedly usable, it should be replaced occasionally since carrier tends to loose its charging ability and to be ground into minute particles because of abrasion after long use.
For the replacement of developer, the underside of the main body of the developing unit is provided with a discharge opening with a lid, and the upper side of the main body is provided, at one end thereof, with a small-diameter supply opening with a cap (or plug). The replacement is practically carried out with the following procedure: the lid of the discharge opening is first opened, and with a recovery container being interconnected to the main body of the developing unit through a duct, the stirring paddles are rotated, so that used developer is forced out from the main body into the recovery container. After the discharge opening has been closed with the lid, the supply opening is opened in order that fresh developer is dropped from the developer container into the main body with the help of a funnel or duct.
For supplementing toner to the main body of the developing unit, the following procedure is taken: With a toner cartridge being mounted on the upper side of a toner hopper, a sealing member adhered to cover the opening of the toner cartridge is stripped off, thereby allowing toner to fall into the toner hopper through the opening. In this case, the length of the sealing member is twice the length of the opening of the toner cartridge or more, and the sealing member is folded such that the portion which is not adhered to the opening turns back outwardly and overlaps along the lengthwise direction of the opening. In order to strip the sealing member off, the end of the portion of the sealing member, which is adhered to the outer side of the toner cartridge, is pulled by the user so that the portion adhered to the opening can be stripped off.
The toner cartridge arranged in such a configuration, however, has the problem that while the sealing member is being stripped off, the face of the sealing member facing to the inside of the toner cartridge is directed downwards and toner sticking to the face of the sealing member comes off and flies in all directions with the result that the surroundings of the apparatus is contaminated.
An attempt to overcome the foregoing problem is disclosed in Japanese Patent Publication Laid-Open No. 3-102371 (1991), wherein there is provided a covering member through which the outwardly folded portion of the sealing member is movably inserted and which covers the adhesive part of the sealing member having extended over the opening, when the sealing member is stripped off.
The above prior developing unit still has the various disadvantages such as described below in the replacement of developer.
Concretely, since the prior developing unit is designed such that the bore of the supply opening provided in the main body of the developing unit is not large and moreover the supply opening is disposed at one end of the main body, it does not have a good operating performance for filling the main body with fresh developer and therefore a pretty long time is required for filling. Another problem is that in order to avoid such a situation that the developer supplied is unevenly accumulated in the main body of the developing unit, it is necessary to carry out the filling operation with the stirring paddles being rotated. This is a disadvantage in energy saving.
A further problem Is that minute dust particles such as toner are likely to scatter around during the filling of fresh developer so that the surroundings of the apparatus and user's hands become dirty.
Further, containers for fresh developer are discarded after the filling operation, and this could be disadvantageous in terms of increasing the efficiency of utilizing natural resources. In this respect, it is possible to re-use a container which have been used for fresh developer for storing used developer, however, a space becomes necessary for setting such an empty container aside until used developer is recovered. This gives rise to another problem of space saving.
The prior art disclosed in the above publication also has a problem in the supplement of the toner. Specifically, a great tension force is necessary for pulling the sealing member, since the sealing member and the cover member are so composed that they are moved respective to each other when the sealing member is pulled and fractional resistance is applied to the cover member.